The long-term goal of our studies is to elucidate the molecular mechanisms of cell-cell interactions during vertebrate development. This proposal focuses on the Hedgehog (Hh) signaling-pathway, which plays a key role in many developmental events. Mutations in members of the pathway are associated with the development of cancer, including basal cell carcinoma, the most prevalent cancer in Western countries, and a seemingly unrelated number of human syndromes and malformations, such as holoprosencephaly and polydactyly. Consequently, understanding how a Hh signal is received, transduced and modulated will be critical to understand how cells proliferate, differentiate or survive in response to the Hh signal, as well as how deregulated Hh signaling leads to diseases. These studies will also make it possible to perform prenatal genetic diagnosis and help design rational therapies for treating these Hh signaling-related diseases. Our general strategy is to focus on three membrane proteins, Hedgehog-interacting-protein (Hip), Patched (Ptch) and Smoothened (Smo), essential for transducing/modulating the Hh signal. The overall goals for this proposal are to define the role of Hip and Ptch in mammalian development through genetic analysis; to define the molecular interactions between Hip, Ptch and Smo in transducing/modulating Hh signal; and to identify missing components in the Hh pathway. 1. To define Hip's role in Hedgehog signaling during mammalian development. A genetic approach utilizing transgenic knockout mice will be taken to dissect the distinct and overlapping roles Hip and Ptch play in modulating Hh signaling during mammalian development. 2. To elucidate the molecular interactions between the three known components of the Hh signaling pathway, Hip, Ptch and Smo, in transducing/modulating the Hh signal. Biochemical and cell culture approaches will be taken to investigate the molecular interactions between Hip, Ptch and Smo in transducing/modulating the Hh signal. 3. To use Hh-responsive cell lines, in combination with expression cloning and candidate gene strategies, to identify missing components in the Hh signaling pathway.